1. Field of the Invention
The present invention relates in general to a method and apparatus adapted for writing information on magnetic storage media in the form of a magnetic disk, and more particularly to such method and apparatus, wherein the magnetic disks have sector-identification fields identifying individual sectors of each recording track, and wherein a simple single-gap magnetic recording head is used for writing and reading operations.
2. Discussion of the Prior Art
As shown in FIG. 15, a magnetic disk 1 such as a floppy disk has a multiplicity of concentric recording tracks 2 (only one track shown in the figure). Each track 2 has an index position at which an index pulse 10 is generated to indicate a start position of the track 2. The track 2 has a preamble portion 3 starting with the index position, a plurality of arcuate sectors 4 (nine sectors of equal length, in this specific example) following the preamble portion 3, and a trailer portion 5 between the last sector 4 and the index position. Each of the sectors 4 includes a sector-identification field (hereinafter referred to as ID field) 6 storing sector identification data (sector address, etc.) identifying the particular sector, and a data field 7 in which information is written. To allow for variations in the position of the data field due to angular positioning errors and dimensional errors, difference or changes of the disk 1, there are provided a leading and a trailing gap 8, 8 between the ID field 6 and the leading and trailing ends of the data field 7. When a blank magnetic disk 1 is initially used, the disk 1 is initialized to prerecord the format described above, on all of the recording tracks 2 provided between the inner central portion of the disk 1 and its outer periphery.
Misalignment of a magnetic recording head with respect to a given track in the radial direction of the magnetic disk 1, will cause remnant signals being left when new information is written on a previous recording on the track. In this case, the remnant signals may be read when the newly written information is read by the magnetic head. To avoid this inconvenience, there has been proposed to provide a guard band or erase track 9, 9 on both sides of the track 2. This guard band or erase track 9 may easily be formed by using a so-called "tunnel-erase" magnetic head with exclusive tunnel erase gaps. However, when it is desired to use a less expensive single-gap magnetic head having a simple construction, the head must be positioned to offset erase positions on both sides of the track 2, for providing the erase tracks 9, 9.
For example, the erase tracks 9, 9 are formed after new information is written on previously recorded information on the track 2. More specifically, the single-gap magnetic head is moved to a first offset position on one side of the newly recorded track 2, which is intermediate between the recorded track 2 and one of the two adjacent tracks. Then, the head is moved to a second offset position intermediate between the recorded track 2 and the other adjacent track. Since the magnetic head located in the first and second offset positions cannot read the sector identification data in the ID fields 6 of the sectors 4, the erase tracks 9, 9 are formed over the entire length of the track 2. Namely, not only the data field but also the ID field of each sector are partially erased at their edge portions.
In the above erasing method, the width of the newly recorded track 2 after the erase tracks 9, 9 are formed is reduced, as compared with the original record width of the track 2 before the erase tracks are formed, as indicated in FIG. 16. In particular, the ID fields 6 whose sector identification data is never re-recorded once initially prerecorded tend to suffer from a progressive reduction in its width during repetitive writing operations on the disk 1 on one recording machine and other machines, due to positioning variations of the magnetic heads relative to the tracks 2 in the radial direction of the disk 1. Therefore, the tolerances in the level of the recorded signals obtained upon reading thereof and in the positioning accuracy are accordingly diminished, causing a problem where the magnetic disks 1 are interchangeable in different recording systems. To maintain a high level of interchangeability of the magnetic disks 1, the recording systems must provide a sophisticated arrangement for positioning the magnetic head relative to the disks.